While there is an option to import choices from Seasons 1 and 2, because of an error I was not able to so I was forced to create a new backstory. What differences this will make for people reading these solutions, I can't say. None of the achievements are missable and you'll get them anyway, but your experience may differ somewhat from mine. I'll keep these solutions as general as possible to account for that.
The story begins with a long cinematic that takes place shortly before the outbreak as two brothers, Javi and David, reunite after Javi's unexplained absence.
After a few dialogue choices...
After a couple more dialogue choices, Javi and company are headed down the road in a van.
A long conversation between Javi and David's wife Kate ensues until they reach a salvage yard and the chapter ends.